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I have a B&S 21 hp v twin that won't stop spining as long as the Battery is connected, even when the key is off and removed, the gear wheel dose disengaege from the fly wheel. My father (elec. engineer for GM) tested the starter relay and seemed to test ok. Not sure what else could be sending power to the armature for the starter, we did install new ignition switch, can any one guide me?
 

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sounds like u have a bad starter solenoid. should b bolted on the cowel somewere. positive cable goes to it .
 

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sounds like u have a bad starter solenoid. should b bolted on the cowel somewere. positive cable goes to it .
It does sound like a bad starter solenoid, but there is also a clue that you put a new ignition switch in. All switches are not the same.

Follow the cable from the positive side of the battery down to the solenoid. The solenoid itself is about 1.5" in diameter and 2 or so inches long (and is usually black plastic but sometimes a metal can).

There will be 2 large large (like 1/4-20 nut size) studs sticking out of it and typically one small wire. One stud carry power from the battery to a contact, the other stud is the other contact and goes to the starter. The little wire is what trigger the contacts to close. During cranking it is 12 volts, all other times it is an open circuit (ie: 0 volts but not ground either).

So, how to diagnose the solenoid.

First, with the + side of the battery disconnected, Disconnect the small wire and put some tape on it so it does not short to anything. Then briefly touch the positive battery cable to the battery. If the starter spins then you have a bad solenoid. You may be able to get a replacement at the auto parts store.

If the starter does not spin, then the little wire probably is hot (and it should not be). Since you installed a new ignition switch it may very well be that the switch is not the correct one. There are several switches and they are internally wired differently. Put a test light (or volt meter) from the little wire to ground. With the key off it, and even in run mode, should be 0 volts. It should only have power on it in the crank mode. If it's not, the new switch is probably the culprit.

I am not sure of your model, but take a look at page 20 of this manual.
http://www.mytractorforum.com/images/reference/H-16Manual.pdf

It may give you some insight on how the power runs through the switch and to the solenoid.

Good luck.
Stuart
 
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